The following documents present the technological background of installations for transporting loads.
More precisely, Document GB 2 437 407 discloses the existence of a system provided with a hook for suspending a load, and means for detaching the load.
Document EP 0 259 250 shows a helicopter having suspended therefrom a container that is provided with stabilizers.
Document FR 2 149 777 presents a system for stabilizing an external load beneath an aircraft, making provision to act on the flying controls in order to enable the aircraft to perform correcting movements.
Document FR 2 575 550 presents a system that acts in real-time to deliver the weight supported by the release-hooks that have an external load stowed thereto.
Document JP19960101019 describes a winch suitable for limiting the accelerations imparted to a body suspended from the winch by a sling.
Document GB 1 074 465 presents a device for limiting the swing angle of a sling fastened to a winch and relative to the gravity axis.
The same applies to Document U.S. Pat. No. 3,904,156, which makes provision for actuators to act on a rigid sling.
Finally, Document FR 2 197 766 provides for explosive means to release the hook that supports the load and to cut through the sling.
It can be seen from the prior art that implementing a sling secured to the structure of a rotorcraft is not without danger.
Firstly, untimely releases of the supported load can be observed, which releases may give rise to consequences that are unfortunate firstly for any elements lying on the trajectory followed by said external load, and secondly for the rotorcraft itself, in so far as the release might possibly and unfortunately lead to the sling whipping back suddenly towards the rotorcraft.
A release-hook is generally controlled either electrically, or else mechanically by means of a mechanical transmission system. A fault in such a mechanical transmission system thus sometimes leads to untimely jettisoning.
Secondly, in the event of the external load or the sling catching onto an obstacle on the ground, the helicopter becomes blocked. Because of the inertia of the rotorcraft, high forces are exerted on the sling. These forces lead to the sling braking, thereby releasing the rotorcraft.
Nevertheless, given the very sudden nature of such a maneuver, the angle of incidence of the disk constituted by the rotor blades rocks rearwards during a transient stage. The blades and then run the risk of striking into, or even of cutting through, the tail boom of the rotorcraft.
Finally, thirdly, after untimely un-hooking or after the sling has broken, the portion of the sling that remains connected to the rotorcraft tends to whip rapidly upwards and thus runs the risk of tangling with the rotor of the rotorcraft.